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Diabetes mellitus strikes 1 in 400 cats and a similar number of Dogs. Symptoms in Dogs and cats are similar to those in humans. Generally, most Dogs and about half of cats experience type-1 (insulin-dependent) diabetes, rather than the type-2 that's now becoming common in obese humans. The condition is definitely treatable, and need not shorten the animal's life span or life quality. In cats, prompt effective treatment can even lead to diabetic remission, in which the cat no longer needs injected insulin. Untreated, the condition leads to blindness in Dogs, increasingly weak legs in cats, and eventually malnutrition, ketoacidosis and/or dehydration, and death.
Cats and Dogs will generally show a gradual onset of the disease over a few weeks, and it may escape notice for a while. The condition is unusual in animals less than 7 years old. The first obvious symptoms are a sudden weight loss or gain, accompanied by excessive drinking and urination. Appetite is suddenly either ravenous (up to 3 times normal) or absent. In Dogs, the next symptom is vision problems and cataracts, while in cats the back legs will become weak and the gait may become stilted or wobbly. A quick test at this point can be done using keto/glucose strips (the same as used on the Atkins diet) with your pet. If the keto/glucose strips show glucose in the urine, diabetes is indicated. If a strip shows ketones in the urine, the pet should be brought to an emergency clinic right away.
Watch for noticeable thinning of the skin and apparent fragility -- these are also serious and indicate that the pet is consuming all its body fat. Dehydration is also common by this point, and death can follow quickly.
Diabetes can be treated but is life-threatening if left alone. Early diagnosis and treatment by a qualified veterinarian can help, not only in preventing nerve damage, but in some cases, in cats, can even lead to remission.[1][2]
Diet is a critical component of treatment, and is in many cases effective on its own. For example, a recent mini-study[3] showed that many diabetic cats stopped needing insulin after changing to a low-carbohydrate diet. The rationale is that a low-carb diet reduces the amount of insulin needed and keeps the variation in blood sugar low and easier to predict. Also, fats and proteins are, in Dogs and perhaps cats, turned into blood glucose much more slowly and evenly than carbohydrates, reducing blood-sugar highs right after mealtimes.
Latest veterinary good practise is to recommend a low-carb diet for cats, and a high-fiber, moderate-carb diet for Dogs. In Dogs another alternative is to feed a normal healthy diet but give mealtime insulin bolus supplements.
It's now becoming clear that lower carbohydrate diets will significantly lower insulin requirements for diabetic cats. Carbohydrate levels are highest in dry cat foods (even the expensive prescription types) so cats are best off usually with a low-carb healthy canned diet. Some prescription canned foods made for diabetic cats are effective, but some ordinary ones work just as well. Between 3 and 9% calories from carbohydrates seems to be optimal. These lists of common commercial cat foods and their carbohydrate energy content are kept up-to date.
Oral medications like Glipizide that stimulate the pancreas promoting insulin release, (or in some cases, reduce glucose production) work in some small proportion of cats (Most Dogs are Type I diabetics so oral hypoglycemic drugs are usually not prescribed for them), but these drugs may be completely ineffective if the pancreas is not working. Worse, these drugs have been shown in some studies[4] to damage the pancreas further, reducing the chances of remission for cats. They have also been shown to cause liver damage. Many are reluctant to switch from pills to insulin injections, but the fear is unjustified; the difference in cost and convenience is minor, (many cats are easier to inject than to pill!) and injections are more effective in almost all cases.
Humans with Type-1 diabetes are often treated with a "basal plus bolus" method, where a long-acting insulin is injected once or twice daily to provide a "basal" insulin level, then shorter-acting insulin is used just before mealtimes. For cats and Dogs a "basal" method is usually employed instead -- a single slow-acting dose, twice daily, attempts to keep the blood sugar within a recommended range for the entire day. In this case it's important for the pet to avoid large meals, since they can seriously affect the blood sugar. (Meals may also be timed to coincide with peak insulin activity.) Once-daily doses are not recommended for most cats, since insulin usually metabolizes faster in cats than in Dogs or humans; an insulin brand that lasts 24 hours in people may only be good for about 12 in a cat.
Cats and Dogs may be treated with animal insulins (pork-based seems to work best in Dogs, beef-based in cats), or with human synthetic insulins. The best choice of insulin brand and type varies between pets and may require some experimentation. One of the popular human synthetic insulins, Humulin N /Novolin N/ NPH, is reasonable for Dogs, but is usually a poor choice for cats, since cats' metabolisms run about twice as fast. The Lente and Ultralente versions were therefore very popular for feline use until summer 2005, when Eli Lilly and Novo Nordisk both discontinued them.
Until the early 1990's, the most recommended type for pets was beef/pork-derived PZI, but that type was phased out over the 1990's and is now difficult to find in many countries. There are sources in the US and UK, and many vets are now starting to recommend them again for pets.
Caninsulin, known in some countries as Vetsulin, made by Intervet (owned by Akzo Nobel), is a brand of pork-based insulin, which is designed for cats and Dogs, and is only available through veterinarians, unlike most other insulin brands, which are designed for people and available to pet owners through pharmacies with a veterinarian's prescription[5]. Since it was never sold to humans, its market share was less harmed by the introduction of human synthetic insulin. Though not its original purpose, in some jurisdictions, it is also approved for use in pet rabbits.
Two new ultra-slow time-release synthetic human insulins are just becoming available in 2004 and 2005 for improving basal stability, generically known as Insulin Detemir ("Levemir")[6] and Insulin Glargine ("Lantus"). A mini-study at the University of Brisbane, Australia[7] has had remarkable results with Insulin Glargine in cats. No studies have yet been performed on pets with Detemir/Levemir, but early anecdotal evidence[8] shows that it is also very effective on cats.
The weak legs syndrome found in many diabetic cats is a form of neuropathy, in particular caused by damage to the myelin sheath of the peripheral nerves caused by glucose toxicity and cell starvation. (There are other conditions that can cause weak legs too, consult your vet before assuming neuropathy.) Most common in cats, the back legs become weaker until the cat displays "Plantigrade stance", standing on its hocks instead of on its toes as usual. The cat may also have trouble walking and jumping, and may need to sit down after a few steps. Some recommend a form of vitamin B12 called methylcobalamin to heal the nerve damage. Neuropathy often heals on its own within 1 to 3 months once blood sugar is regulated, but anecdotal evidence points to a faster recovery rate with these supplements.
Dogs' eyes are highly sensitive to high blood sugar, and will have blurred vision, cataracts, or even total blindness after as little as a few days at blood glucose concentration above 16.7mmol (300 mg/mL). Cataracts may be treated later, but blindness is permanent in some cases. Fortunately, Dogs rely more on smell and hearing than on vision, and so may surprise you with how well they get along without their eyes.
Cats and Dogs may in some cases have their mealtimes strictly scheduled and planned to match with injection times. In other cases where the pet free-feeds and normally eats little bits all day or night, it may be best to remain on this schedule and try to use a very slow-acting insulin to keep a constant level of blood glucose. Consult your veterinarian. Note that some veterinarians still use the outdated recommendation of using Humulin "N" or NPH insulin for cats. This insulin is too fast-acting for most cats (though fine for Dogs and humans). Cat metabolism runs about twice as fast as human, and the often-effective slower-acting Lente and Ultralente (Humulin L and Humulin U) insulins are being discontinued (as of 2005), so most cats are now using either the veterinary PZI insulins, or the new full-day analogs glargine (Lantus) and detemir (Levemir).
The goal at first is to "regulate" the pet's blood glucose, which may take a few weeks or even many months. This process is basically the same as in type-1 diabetic humans. The goal is to keep the blood glucose values in a comfortable range for the pet during the whole day, or most of it.
The recommended method is to Start Low - Go Slow:
Absolute numbers vary between pets, and with meter calibrations. The numbers below are as shown on a typical home glucometer, not necessarily the more accurate numbers a vet would see. For general guidelines only, the levels to watch are approximately:
| mmol/L | mg/dL(US) | |
| 2.2 | 40 | Readings below this level are usually considered hypoglycemic. Treat immediately |
|---|---|---|
| 3 | 54 | this is an average non-diabetic pet's level, but leaves little margin of safety for a diabetic. |
| 5 | 90 | a common minimum safe value for the lowest blood sugar of the day |
| 6-10 | 100-180 | desired range for diabetics (non-diabetic range is 2.2 - 7.5, (40-130) but usually unsafe to aim for) |
| 11-15 | 200-270 | "Renal threshold" (varies between individuals) excess glucose from the kidneys spills into the urine, pet begins to show diabetic symptoms. Long term damage to eyes, nerves, pancreas and other organs if glucose remains above here too often. Risk of Urinary tract infection over time. |
| 14 | 250 | approximate maximum safe value for the highest blood sugar of the day, in Dogs, to avoid short-term eye damage. |
| 16.7 | 300 | approximate maximum safe value for the highest blood sugar of the day, in cats, to avoid short-term nerve damage. |
| 20 | 360 | At high readings like this, combined with an infection, dehydration, or a fast, animals can sometimes quickly develop Diabetic ketoacidosis which is immediately life-threatening. Always check urine for ketones at high readings. |
The regulation process is described in more detail here.
It's confusing but true: Too little insulin means pre-shots are too high; too much insulin often also means pre-shots are too high. This effect is often noted by those who test their pets' blood glucose at home.
The reason: Anytime the glucose level drops too far or too fast, the cat or Dog may defensively dump glucose (converted from glycogen in the liver), as well as hormones epinephrine and cortisol, into the bloodstream. (If these are insufficient, hypoglycemia ensues!) The glycogen raises the blood glucose, the other two may make the pet insulin-resistant for a day or two. This phenomenon was first documented by a Dr. Somogyi.[10] [11].
Even when raising the insulin dose slowly and carefully, it's possible to pass the correct dose and go on to an overdose. (A typical case is increasing bidaily dosage from 1 unit to 2, passing a correct dose of 1.5 units.) This may produce a rebound -- a swift jump in blood glucose up from a dangerously low reading, to beyond the previous pre-shot level. The pet may be a bit less responsive to the same dose the next shot, from those other hormones. Repeating the overdose on subsequent days, and checking only pre-shot readings or urine glucose, can give the dangerously wrong impression that more insulin is needed! Remember to check occasionally at the expected nadir (low point) as well.
It's unusual to be monitoring glucose right when this happens, and typical to just continue the overdose, leading to a repeated rebound situation. So it's good to learn to recognize the patterns of repeated rebound.
According to recent experience on internet diabetes forums, the rebound phenomenon may be less dramatic and more common than usually thought, in some pets. The term "mini-rebound" is beginning to gain currency. If your insulin dose is just a smidgen high, you may see either nothing at all, or a hypoglycemic episode or a mini-rebound. Some Feline Diabetes Message Board regulars describe mini-rebounds here: [12]
It's not always easy to tell a rebound from a regular curve showing insulin action ending normally. One way to tell the difference is to take a "curve" (repeated tests every 2 hours starting with the insulin shot) on a weekend and look for the shape of the curve. If the curve is valley-shaped, and gradual, then you are not seeing Somogyi rebound. Other shapes should arouse suspicion. In particular, if the rise after peak action is faster and rises higher than the original pre-insulin level and the original fall in blood sugar, you have good cause to consider rebound. The only sure way to check is to reduce dosage and look for a better-shaped curve.
A fairly sure sign: Anytime blood glucose numbers seem higher after dosage is raised, consider the possibility of a somogyi rebound. But other things can cause unexpectedly high blood glucose too, so look for a clear correlation with dosage changes.
An acute hypoglycemic episode (very low blood sugar) can happen even if you are careful, since pets' insulin requirements sometimes change without warning. The symptoms are depression/lethargy, confusion/dizziness, loss of excretory/bladder control, vomiting, and then loss of consciousness and/or seizures. As soon as possible, administer honey or corn syrup by rubbing it on the gums (even if unconscious, but not if in seizures), and rush it to the vet. Carry more honey or corn syrup with you on the way and keep rubbing it on the gums, where it can be absorbed -- it could save the pet's life. Every minute without blood sugar causes brain damage. (Some recommend administering syrup anally if the animal is in seizures!)
If the pet has hypoglycemia according to the blood glucose meter (<2.2mmol/L or 40mg/dL), but no symptoms, give treats or food if possible. If they won't eat, try putting food in their mouth. If that doesn't work, administer some honey followed by food or cat treats, and continue to do so until the blood glucose is rising, and the latest insulin shot's peak action is past.
Sometimes a mild hypoglycemic episode will go unnoticed, or leave evidence such as an "accident" where kitty fails to make it to the litterbox. In these cases the blood sugar will probably appear paradoxically high upon the next test hours later, since the pet's body will react to the low blood sugar by stimulating the liver to release stored glycogen. This condition is known as Somogyi rebound (see link above), and requires a lowered insulin dosage for the next few days. The Somogyi rebound may also occur when the pet's blood glucose drops too rapidly, even if it never actually reaches a low reading.
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